Altered fatty acid composition is found in blood and tissue lipids of patients with cystic fibrosis. These alterations are more commonly found in CF patients with malabsorption and mal-digestion, but are occasionally observed in CF subjects with normal pancreatic function. Recent investigations suggest that the lower caloric intake of the CF patient relative to the caloric requirements may lead to increased utilization of absorbed essential fatty acid (i.e. linoleic acid). Such increased metabolism of linoleic acid would in part explain the altered fatty acid composition observed. More importantly, the decreased linoleic acid content as observed in most CF patients is associated with decreased unsaturation in tissue phospholipids and membranes. Accordingly, a linoleic acid absorption test was devised and performed. Patients with CF were capable of absorbing linoleic acid from all preparations studied. It is concluded that malabsorption alone cannot explain the abnormal fatty acid patterns in CF patients.